Don't worry about the wet weather.
There is practically not that big a difference between wet and dry season in Singapore.
It can rain anytime, any day. Just find shelter (not a problem)
For lenses, just bring the typical ones from UWA to short tele.
Mine varies from 10-20 or DA15; 24/35/40/43mm; 77ltd/85/135mm
Stock up on $$$.
Pentax stuff can be very well priced here and some of the new stuff are sold here before anywhere else outside Japan (K30 avaliable in shops in 10days).
You can link up with the local Pentax community here :
Pentax
there is a monthly outing too, so do join if you can.
There are plenty of places to travel to within a few hours car/coach or by plane.